Title: Dynamics of the lignin glass transition

Abstract

The dynamics of lignin, a complex and heterogeneous major plant cell-wall macromolecule, is of both fundamental and practical importance. Lignin is typically heated to temperatures above its glass transition to facilitate its industrial processing. Here, we performed molecular dynamics simulations to investigate the segmental (α) relaxation of lignin, the dynamical process that gives rise to the glass transition. It is found that lignin dynamics involves mainly internal motions below T_g, while segmental inter-molecular motions are activated above T_g. The segments whose mobility is enhanced above T_g consist of 3–5 lignin monomeric units. The temperature dependence of the lignin segmental relaxation time changes from Arrhenius below T_g to Vogel–Fulcher–Tamman above T_g. This change in temperature dependence is determined by the underlying energy landscape being restricted below T_g but exhibiting multiple minima above T_g. The Q-dependence of the relaxation time is found to obey a power-law up to Q_max, indicative of sub-diffusive motion of lignin above T_g. Temperature and hydration affect the segmental relaxation similarly. Increasing hydration or temperature leads to: (1) the α process starting earlier, i.e. the beta process becomes shortened, (2) Q_max decreasing, i.e. the lengthscale above which subdiffusion is observed increases, and (3) the number of monomers constitutingmore » a segment increasing, i.e. the motions that lead to the glass transition become more collective. The above findings provide molecular-level understanding of the technologically important segmental motions of lignin and demonstrate that, despite the heterogeneous and complex structure of lignin, its segmental dynamics can be described by concepts developed for chemically homogeneous polymers.« less

Authors:

Vural, Derya  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-0120-3024"
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Smith, Jeremy C.  ^[2];

• Search DOE PAGES for author "Smith, Jeremy C."
• Search DOE PAGES for ORCID "0000-0002-2978-3227"
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Petridis, Loukas  ^[2]

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• Search DOE PAGES for ORCID "0000-0001-8569-060X"
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+ Show Author Affiliations

1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). UT/ORNL Center for Molecular Biophysics (CMB); Univ. of Tennessee, Knoxville, TN (United States). Dept. of Biochemistry and Cellular and Molecular Biology; Giresun Univ. (Turkey). Dept. of Physics
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). UT/ORNL Center for Molecular Biophysics (CMB); Univ. of Tennessee, Knoxville, TN (United States). Dept. of Biochemistry and Cellular and Molecular Biology

Publication Date:

2018-07-18

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division

Contributing Org.:

Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)

OSTI Identifier:

1471833

Alternate Identifier(s):

OSTI ID: 1461709

Grant/Contract Number:  

AC05-00OR22725; FWP ERKP752; AC02-05CH11231

Resource Type:

Accepted Manuscript

Journal Name:

Physical Chemistry Chemical Physics. PCCP

Additional Journal Information:

Journal Volume: 20; Journal Issue: 31; Journal ID: ISSN 1463-9076

Publisher:

Royal Society of Chemistry

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 59 BASIC BIOLOGICAL SCIENCES; 09 BIOMASS FUELS